Emerging and reemerging infectious diseases continue to pose serious health threats world-wide. Consequently, the development of measures to mitigate the natural, as well as potential bioterrorist threats of these infectious diseases is an important endeavor. The NIAID Strategic Plan for Biodefense Research is specifically directed at promoting research that can provide solutions to mitigate the threat posed by Category A, B, and C priority pathogens. The development of vaccines against these pathogens provides a strategy to mitigate the potential threat. Crimean-Congo hemorrhagic fever virus (CCHFV) is a significant human pathogen due to it ability cause severe disease and its high fatality rate. CCHFV is classified as a category C priority pathogen due the concern that it could be used as a biological agent. There is currently no effective vaccine or therapy that is widely available to mitigate such a threat. New technologies and production methods may offer the most effective responses to such disease threats. The proposed research aims to develop a vaccine to protect against disease caused by infection with CCHFV using a stable insect cell line expression platform that has previously been used to produce vaccine candidates for other priority pathogens. The platform is based on the production of recombinant subunit proteins that maintain structural and immunogenic integrity. Candidate vaccines against dengue and West Nile virus have already been produced in this system and both have entered clinical trials. Thus, this platform can be scaled for cGMP production and meet FDA regulatory requirements. The expression of the CCHFV Gn and Gc envelope glycoprotein will be evaluated. The complex nature of viral envelope glycoproteins presents challenges in designing and expressing recombinant subunits that maintain native-like structure. The platform proposed for use in this project has the demonstrated capability of producing complex viral envelope proteins with native-like conformation. Successfully expressed recombinant products will be evaluated for immunogenic potential using two novel adjuvant formulations that have dose sparing potential. Based on immunogenicity studies, selected combinations of recombinant proteins and adjuvant will be evaluated in protective efficacy studies utilizing a recently developed mouse challenge model for CCHFV. In addition to vaccine development, the protein subunits produced can be used for development of diagnostic reagents, as well as targets for antiviral drug development. The successful development of a CCHFV vaccine utilizing this stable insect cell platform will not only meet the need for a safe and effective vaccine against CCHFV, it will also help to demonstrate the utility of the platform and pave the way for the development of additional vaccines against NIAID viral priority pathogens.